B08 140G0221R0007 Attch 1 PWS.pdf

AGREEMENT NUMBER

Attachment A Statement of Work

USGS OKI WATER SCIENCE CENTER

CONSTRUCTION OF A

MONITORING WELL NETWORK FOR SUSTAINABILITY PROJECT

INDEX TO TECHNICAL SPECIFICATIONS

1.0 Scope and Locations

2.0 special conditions

3.0 Responsibility

4.0 Applicable Codes and Regulations

5.0 Standard Specifications

6.0 Permits and Licenses

7.0 Materials

8.0 Storage of Materials

9.0 Protection of Existing Works

10.0 Unforseen Obstacles

11.0 Local Conditions

12.0 Well Drilling

13.0 Well Casing and Screen Installation

14.0 Annular Space sandpack Material

15.0 Cement/Bentonite Grout

16.0 Plumbness

17.0 Temporary Fence

18.0 Clearing and Grubbing

19.0 Topsoil

20.0 Seeding

21.0 Site Cleanup

Solicitation 140G0221R0007 Attachment 1

1.0 SCOPE AND LOCATIONS

• The U.S. Geological Survey (USGS) Ohio Kentucky Indiana Water Science Center (OKI WSC) requires the drilling of four water-level monitoring wells

• The contractor shall provide drilling and construction of up to a known need of 4 boreholes and 4 monitoring wells with an option for additional boreholes and monitoring wells depending on funds availability in support of a research project. Funding will be limited to a cap.

• The contractor shall include the furnishing of all labor, material, equipment, supplies and incidentals necessary for the construction of each monitoring well for the work to be performed under this contract. The work shall include the following:

A. Well drilling, installation of casing and well screen, filter pack, grouting, well development.

B. Installation of a protective riser and a concrete pad, site clean-up, and site restoration.

• Site locations are in northwestern Ohio. A map showing the locations of the proposed sites is attached. The table below includes specific location information and their depths:

Proposed Well Number

Well Location

Estimated well depth, in feet BLS MIO-1 41°38'16"N, 84°44'46"W ~300 to 400 MIO-2 41°23'03"N, 84°44'06"W ~300 to 400 MIO-3 41°39'57"N, 84°26'15"W ~300 to 400 MIO-4 41°28'00"N, 84°48'02"W ~300 to 400

• The Contractor shall adhere to local noise and light ordinances, if they exist. Weekend work is to be avoided.

• The Contractor shall keep the site free of debris and shall remove all trash from the site daily. The entrance way to the monitoring well site shall be kept free of rubbish, dirt and other material.

A. The contractor shall take photos at the beginning and end of each workday to document the condition of the site before drilling, following conclusion of the workday, and the condition of the site following completion of work. The contractor shall email photos daily while work is being completed.

3.0 RESPONSIBILITY

• All responsibility for the entire work and accidents occurring therewith shall rest with the Contractor constructing the Work until its completion and acceptance.

• The Contractor shall comply with the U.S. Department of Labor Safety and Health Regulations for construction promulgated under the Occupational Safety and Health Act of 1970 (See attached file: OSHA_PL91-596.pdf) as currently amended; and under Section 107 of the Contract Work Hours and Safety Standards Act (PL 91-54), as currently amended, as a minimum requirement. In the event of conflict among said Safety and Health Regulations, the Contract Document and requirements of other regulatory agencies, the most stringent provisions shall be binding on the Contractor.

• In order to protect the lives and health of his employees under this Contract, the Contractor shall comply with all pertinent provisions of the "Manual of Accident Prevention in Construction", issued by the Associated General Contractors of America, Inc., and shall maintain an accurate record of all cases of death, occupational disease, and injury requiring medical attention, or causing loss of time from work, arising out of and in the course of employment on work under the Contract. Contractor alone shall be responsible for the safety, efficiency and adequacy of his plant, appliances, and methods, and for any damage, which may result from their failure or improper construction, maintenance, or operation.

• The selection of levels of personnel protective equipment is an iterative process based upon site specific conditions and available data. When no respiratory or dermal hazards exist, the Contractor shall proceed with a minimally protective work uniform consisting of coveralls, reinforced work boots, hard hats and when needed gloves, ear, and eye protection. Although not anticipated at these sites, should the necessity for additional personnel protective equipment arise at Levels C or D, the Contractor shall proceed accordingly and be prepared to supply such additional protection for Contractor’s employees.

• The contractor assumes all responsibility for loss or damage of equipment owned or operated by the Contractor, his agents, or employees or subcontractor or for the injury to or death of the Contractor, or his agents or employees, or his subcontractor. The Contractor shall hold and save the USGS OKIWSC, its officers, agents, servants and employees harmless from liability of any nature or kind for or on account of the use of any copyrighted or uncopyrighted composition, secret process, patented or unpatented invention, articles or appliances, used in the performance of this Contract, including their use by the USGS OKIWSC unless otherwise specifically stipulated in the Contract. The Contractor shall be responsible for any negligent or wrongful acts or omissions of the Contractor, his employees, agents or subcontractors and employees or agents of the subcontractor(s) incident to the performance of this Contract. The Contractor shall hold and save the USGS OKIWSC, its officers, and employees harmless from all liability for any death or damage to persons or to real or personal property, including negligent use of materials used in conjunction with, or incident to, equipment furnished by the Contractor, or otherwise incident to performance of the Contract. The Contractor shall not be responsible for any negligent or wrongful acts or omissions of the USGS OKIWSC, its employees, cooperators or their employees.

• The omission of the phrase "the Contractor shall" from these detailed Specifications shall not be construed as relieving the Contractor from full and complete performance of the work.

4.0 APPLICABLE CODES AND REGULATIONS

• All work performed by the Contractor shall be in accordance with Federal, State, County and Local Codes and Ordinances.

5.0 STANDARD SPECIFICATIONS

• The contractor shall follow the specifications provided by the Ohio Environmental Protection Agency in Chapter 7 of the Technical Guidance Manual for Ground Water Investigations (See attached file: OEPA_TGM-07.pdf).

6.0 PERMITS AND LICENSES

• The Contractor, and/or subcontractors, shall be registered and bonded through the Ohio Department of Health and shall comply with all regulations and requirements of the Department.

• The Contractor shall procure all licenses or other permits, if any, and pay all taxes, fees, charges and give notices necessary and incident to the lawful prosecution of the work.

7.0 MATERIALS

• The Contractor shall provide all drilling materials

A. All well casing, well screen, well protector, grout, and filter pack materials shall be previously unused and subject to the approval of the USGS OKIWSC. No deviations from the provisions of these detailed Specifications herein shall be made without written approval of the USGS OKIWSC.

B. The contractor shall use materials as described by the Ohio Environmental Protection Agency in Chapter 7 of the Technical Guidance Manual for Ground Water Investigations (See attached file: OEPA_TGM-07.pdf).

8.0 STORAGE OF MATERIALS

• The Contractor shall store materials as to insure the preservation of their quality and fitness for the work. Other private property shall not be used for storage purposes without the written permission of the USGS OKIWSC.

9.0 PROTECTION OF EXISTING WORKS

• The Contractor shall protect all existing structures, piping, utilities, fencing or materials, “herein refer to as properties”, within each site area against damage as may be required by the USGS OKIWSC. The Contractor shall be responsible for any damage to these existing properties during the operations and such damage shall be corrected by replacing the items damaged to their original condition and position at the Contractor's cost and expense to the satisfaction of the USGS OKIWSC.

10.0 UNFORSEEN OBSTACLES

• The Contractor shall remove, demolish and dispose of any boulders, concrete or masonry structures, encountered during drilling in accordance of all federal state and local statutes, regulations laws and codes.

11.0 LOCAL CONDITIONS

• The Contractor shall install all wells on a section of land located on the right-of-way property near each proposed well location. The USGS OKIWSC will designate the general location where work will be performed. After the general location has been established, the Contractor shall call (OHIO811, (800) 362-2764 or 811) for a mark out of all utilities, i.e. electric, gas, water, sanitary sewer, drainage, telephone, irrigation, street lighting, or any other suspected underground appurtenances within the area. Upon mark out completion of all utilities, the Contractor, with the concurrence of the USGS OKIWSC representative, shall determine the actual drilling site, which allows for safe drilling and does not interfere with any underground utilities and appurtenances.

• The Contractor shall obtain potable water for drilling purposes within permitted allowances of local water suppliers.

• The Contractor shall provide his own source of power If there is no available electrical power at a site.

12.0 WELL DRILLING

• The Contractor shall primarily use the mud rotary method to drill 8 to 9.5-inch diameter boreholes for the purpose of installing a monitoring well in the borehole at each site.

A. The contractor shall drill each borehole 5 feet into bedrock. Estimated depth to bedrock at each proposed site is estimated to be between 300 and 400 feet below land surface. The final depths will depend on the depth at which bedrock is encountered during drilling. It is expected that the wells will be drilled into unconsolidated deposits of gravel, sand, silt and clay and weathered bedrock.

B. The Contractor shall provide all well screens and fittings necessary for a complete installation, screen sizes from 0.0010 – 0.0060-inch shall be available for use as determined by the USGS OKIWSC onsite representative to facilitate pumping water free of sand.

• The contractor shall develop each well until the water is clear and free of suspended sediment and pumping at an acceptable discharge rate as determined with the agreeance of the USGS OKIWSC onsite representative. Initial depth to water, constant pumping rate, pumping time, and final depth to water (drawdown) shall be measured during the development of the well and recorded.

• The contractor shall ensure the pipe joints are free from any leakages of water into or from the surrounding formations.

A. If leaks are detected after well pumping, sampling, and cased geophysical logging, the contractor shall backfill and properly abandon the well at no charge to the USGS and replace the well.

14.0 ANNULAR SPACE SANDPACK MATERIAL

• The contractor shall install a sand pack within the annular space surrounding the well screen to a height of 2 ft above the top of the screen.

A. The Contractor shall furnish clean, sound, hard, durable stone conforming to the Ohio Technical Guidance for Well Construction and Ground Water protection (See attached file: OEPA_WellConstructionGuidance.pdf) for use in installing the sand pack. The material shall be placed at the direction of the USGS OKIWSC onsite representative at the depth and thickness between the well casing and outer wall of the annular space. The contractor shall take special care to avoid bridging and the creation of voids during the install.

B. The contractor shall remove obstacles restricting placement of sand or grout along the well casing prior to installation.

15.0 CEMENT/BENTONITE GROUT

• The Contractor shall install a mix of bentonite grout in the annular space between the borehole wall and the well casing above the sand pack to the ground surface to completely grout the annular space. All work shall be as directed by the USGS OKIWSC onsite representative.

A. The contractor shall use a mix of bentonite and cement slurry that complies with standards set in Ohio Technical Guidance for Well Construction and Ground Water protection (See attached file: OEPA_WellConstructionGuidance.pdf). Potable water shall be used for mixing cement grout. A Bentonite additive may be used.

B. The contractor shall circulate drilling fluids to remove any obstruction and open a clear annular space prior to installation.

C. The contractor shall mix and install the cement bentonite slurry in one continuous operation by tremie pipe or pumping. The tremie pipe or any conduit shall extend from ground surface to the level within the annular space as specified by the USGS OKIWSC (generally this level will be within close proximity to the seal above the sand pack material). The grout should be introduced at the base of the grouting interval to minimize contamination or dilution of the slurry and bridging of the mixture with upper-formation material.

16.0 PLUMBNESS

• The contractor shall install each well plumb and true to line with a deviation from the vertical less than six (6) inches per one hundred (100) feet of depth as measured to the full depth of the well. In no event will these requirements be waived.

• The contractor shall furnish all labor, materials, tools and equipment to run a test of plumbness of the completed test hole as directed by the USGS OKIWSC onsite representative. The USGS OKIWSC may require the contractor to run additional tests during the performance of the work to ensure the requirement is met.

17.0 TEMPORARY FENCE

• The Contractor shall furnish and install temporary fence, including fabric, fence posts, etc.

as directed by the USGS OKIWSC onsite representative for safety reasons.

• The Contractor shall protect and maintain the existing temporary fence at the site until the drilling equipment is removed. The Contractor shall then remove and legally dispose of the temporary fence around the well site.

18.0 CLEARING AND GRUBBING

• The contractor shall include all labor, materials, tools and equipment necessary for clearing, grubbing, removing and disposing of all vegetation and debris (including earthen materials incidentally removed with vegetation and debris), and removing structures and obstructions located within the limits shown of the work area or designated by the USGS OKIWSC, except such objects as are designated to remain in place or are to be removed in accordance with other sections of these Specifications.

• The USGS OKIWSC onsite representative shall establish the limits of the work area and will designate all trees, plants, shrubs and other items to remain. The Contractor shall include the preservation from injury or defacement of all vegetation and objects designated to remain.

A. The contractor shall conduct miscellaneous trimming of trees or shrubs designated to remain when directed by the USGS OKIWSC onsite representative. Trimming shall be in accordance with good tree surgery practice.

B. The contractor shall dispose of all vegetation and debris to be removed. The Contractor shall obtain all necessary permits to do so.

C. The contractor shall be responsible for securing waste disposal sites, obtaining written permission of the owner of the disposal site, securing any required permits, and responsible for the cost of securing such sites. The Contractor shall furnish the permit numbers of all required permits for disposal sites.

• The contractor shall be responsible for grubbing all trees, stumps, roots and other objects not designated to remain. If the area is not to be benched, the removal of undisturbed stumps and roots and nonperishable solid objects that will be a minimum of four feet below the embankment surface and that do not extend more than six inches above the original ground line, will not be required.

A. The contractor shall cut off all stumps and nonperishable solid objects permitted to remain in place not more than six inches above the ground line or low water level in areas outside of the grading limits of cut and embankment areas and to the established limits of the Work

B. The contractor shall backfill stump holes and other holes from which obstructions are removed with suitable materials and compacted except in areas to be excavated

C. The contractor shall take care to insure that the grass, moss cover, or the natural ground is not disturbed in areas where Hand Clearing is indicated or designated by the USGS OKIWSC onsite representative. Stumps shall be cut flush with the ground, except that in areas within four feet or more of embankment cover, stumps may be cut off 6 inches above the natural ground.

19.0 TOPSOIL

• The Contractor shall use suitable topsoil stockpiled by the Contractor from the work area and, if additional topsoil is required, the contractor shall provide clean topsoil from off an offsite source.

• The Contractor shall keep all topsoil free from roots and stones, and that portion which cannot be used immediately upon regarded areas is to be piled in neat spoil banks located in the work area as directed by the USGS OKIWSC onsite representative.

• The Contractor shall avoid admixture of subsoil and topsoil while stripping topsoil. If the amount of topsoil on the site is inadequate, the Contractor shall furnish sufficient additional topsoil. No topsoil which has been stripped shall be removed from the site.

• All topsoil shall be as approved by the USGS OKIWSC onsite representative.

20.0 SEEDING

• The contractor shall seed the disturbed area when directed by the USGS OKIWSC onsite representative.

A. No seeding shall be done until the topsoil has been hand raked to the required finished grades.

B. The topsoil shall be smooth, friable and of a uniformly fine texture. No seed shall be sown unless the top surfaces of the seed bed is free of stones larger than ½-inch, roots, weeds, sod or other litter.

C. All seed shall be as approved by the USGS OKIWSC onsite representative.

21.0 SITE CLEANUP

• The contractor shall remove all tools, appliances, surplus materials, temporary drainage, rubbish and debris incidental to the work from site after completion of the work.

• The contractor shall dress backfill excavation and vehicular ruts to conform to the existing landscape or terrain.

• The contractor shall be responsible for the completion of all repairs or the replacement of utilities, structures, roads, fences, or any other pre-existing item damaged or destroyed due to the Contractor’s negligence prior to completion of contract.

• The contractor shall be responsible for the disposal of drill cuttings, rock core, grout or bentonite slurry, and other solid or liquid materials bailed, pump or otherwise removed from the borehole during drilling, well installation and completion procedures within all appropriate regulatory requirements.

• The contractor shall install a protective riser around each well. The USGS will install an instrument box and equipment following the completion of the well on top of the protective riser. An example photo of a completed monitoring well is included.

• The contractor shall install a 3-foot square by 1.5-foot-thick concrete well pad around each protective riser. The cement from the concrete base will extend down the borehole to below the frost line. The contractor shall install an identification and/or survey marker in the concrete pad. This marker will be supplied by the USGS.

Figure 2. Example photo of a completed USGS Groundwater monitoring well following the installation of the instrument box on top of the protective riser.

State of Ohio Environmental Protection Agency

Division of Drinking and Ground Waters

Technical Guidance Manual for Ground Water Investigations

Chapter 7

Monitoring Well Design and Installation

February 2008

Governor : Ted Strickand Director : Chris Korleski

TECHNICAL GUIDANCE

MANUAL FOR

GROUND WATER INVESTIGATIONS

CHAPTER 7

Monitoring Well Design and Installation

February, 2008 Revision 1

Ohio Environmental Protection Agency Division of Drinking and Ground Waters

P.O. Box 1049 50 W. Town Street, Suite 700 Columbus, Ohio 43216-1049

Phone: 614-644-2752 http://www.epa.state.oh.us/ddagw/

TGM Chapter 7: Design and Installation 7-ii Revision 1, February, 2008

PREFACE

This document is part of a series of chapters incorporated in Ohio EPA’s Technical Guidance Manual for Hydrogeologic Investigations and Ground Water Monitoring (TGM), which was originally published in 1995. DDAGW now maintains this technical guidance as a series of chapters rather than as an individual manual. The chapters can be obtained at http://www.epa.state.oh.us/ddagw/tgmweb.aspx

The TGM identifies technical considerations for performing hydrogeologic investigations and ground water monitoring at potential or known ground water pollution sources. The purpose is to enhance consistency within the Agency and inform the regulated community of the Agency’s technical recommendations and the basis for them. In Ohio, the authority over pollution sources is shared among various Ohio EPA divisions, including the Emergency and Remedial Response (DERR), Hazardous Waste Management (DHWM), Solid and Infectious Waste (DSIWM), and Surface Water (DSW), as well as other state and local agencies.

DDAGW provides technical support to these divisions.

Ohio EPA utilizes guidance to aid regulators and the regulated community in meeting laws, rules, regulations and policy. Guidance outlines recommended practices and explains their rationale. The Agency may not require an entity to follow methods recommended by this or any other guidance document. It may, however, require an entity to demonstrate that an alternate method produces data and information that meet the pertinent requirements. The procedures used to meet requirements usually should be tailored to the specific needs and circumstances of the individual site, project, and applicable regulatory program, and should not comprise a rigid step-by-step approach that is utilized in all situations.

TGM Chapter 7: Design and Installation 7-iii Revision 1, February, 2008

MAJOR CHANGES FROM THE FEBRUARY 1995 TGM

The Ohio EPA Technical Guidance Manual for Hydrogeologic Investigations and Ground Water Monitoring (TGM) was finalized in 1995. This guidance document represents an update to Chapter 7 (Monitoring Well Design and Installation). Listed below are the major changes from the 1995 version.

1. Deleted language cautioning against the use of multi-level wells. Added information on multi-level well systems.

2. Added text indicating that vertical water profiles can be obtained with passive sampling techniques.

3. Revised text to state that PVC is preferable to PTFE for monitoring well screens when organics are present. Studies have shown that PTFE sorbs organic compounds at a higher rate than does PVC.

4. Added language stating that a filter pack can be much less thick than previously recommended.

5. Added language describing the use of pre-packed screen wells.

6. Changed the recommendation for selecting the screen slot size of a naturally packed well from a slot that retains 30 to 60% of the filter pack to one that retains 70%.

7. Added information on methods for creating high-solids bentonite.

8. Revised text to note potential problems with using a bentonite/cement mixture. However, the guidance does not rule it out as a potential sealant for monitoring wells. Some literature has indicated problems with the use of a bentonite as an additive to neat cement for well sealing. Because of this, the Ohio rules applying to drinking water wells do not allow the use of a bentonite/cement mixture (OAC 3745-09). However, there are also articles that favor its use, and many states still allow (and recommend) it.

9. Added section on procedures for installation of neat cement grout.

10. Added recommendation that, due to its potential to affect ground water chemistry, bentonite sealing material should be placed a minimum of 3 to 5 feet above the top of the well screen.

11. Included references to new documents that have become available since 1995, including:

Updated existing references.

Added new ASTM reference for installation of pre-packed screens.

Added new ASTM reference for maintenance and rehabilitation of ground water monitoring wells.

Added reference to the Technical Guidance for Ground Water Investigation Chapter

15 - Use of Direct Push Technologies for Soil and Ground Water Sampling.

TGM Chapter 7: Design and Installation 7-iv Revision 1, February, 2008

TABLE OF CONTENTS

PREFACE.............................................................................................................................. 7-ii MAJOR CHANGES FROM THE FEBRUARY 1995 TGM .................................................... 7-iii TABLE OF CONTENTS ....................................................................................................... 7-iv DESIGN OF MULTIPLE-INTERVAL SYSTEMS ................................................................... 7-1

WELL CLUSTERS ............................................................................................................ 7-3 MULTI-LEVEL WELLS ...................................................................................................... 7-3 NESTED WELLS .............................................................................................................. 7-3 SINGLE-CASING, LONG-SCREEN WELLS..................................................................... 7-4

CASING ................................................................................................................................ 7-4 CASING TYPES ............................................................................................................... 7-4

Fluoropolymers .............................................................................................................. 7-4 Metallics ........................................................................................................................ 7-5 Thermoplastics .............................................................................................................. 7-6

TYPE SELECTION ........................................................................................................... 7-6 HYBRID WELLS ............................................................................................................... 7-8 COUPLING MECHANISMS .............................................................................................. 7-8 DIAMETER ....................................................................................................................... 7-9 CASING INSTALLATION .................................................................................................. 7-9

INTAKES ............................................................................................................................ 7-10 FILTER PACK ................................................................................................................. 7-10

Types of Filter Packs ................................................................................................... 7-10 Nature of Artificial Filter Pack Material ........................................................................ 7-11 Dimension of Artificial Filter Pack ................................................................................ 7-12 Artificial Filter Pack Installation .................................................................................... 7-12

SCREEN ......................................................................................................................... 7-15 Screen Types .............................................................................................................. 7-15 Pre-Packed Screen Wells ............................................................................................ 7-16 Slot Size ...................................................................................................................... 7-16 Length ......................................................................................................................... 7-16

OPEN BOREHOLE INTAKES ......................................................................................... 7-17 ANNULAR SEALS .............................................................................................................. 7-17

MATERIALS .................................................................................................................... 7-17 Bentonite ..................................................................................................................... 7-18 Neat Cement Grout ..................................................................................................... 7-18

SEAL DESIGN ................................................................................................................ 7-20 SEAL INSTALLATION .................................................................................................... 7-20

Bentonite ..................................................................................................................... 7-20 Neat Cement ............................................................................................................... 7-21

SURFACE SEAL/PROTECTIVE CASING COMPLETIONS ............................................... 7-22 SURFACE SEAL ............................................................................................................. 7-22 FLUSH-TO-GROUND COMPLETIONS .......................................................................... 7-22

DOCUMENTATION ............................................................................................................ 7-23 MAINTENANCE AND REHABILITATION .......................................................................... 7-24 REFERENCES ................................................................................................................... 7-26

TGM Chapter 7: Design and Installation 7-1 Revision 1, February, 2008

CHAPTER 7

MONITORING WELL DESIGN AND INSTALLATION

To collect representative ground water samples, it is necessary to construct monitoring wells to gain access to the subsurface. This chapter covers installation and construction of single-riser/limited interval wells, which are designed such that only one discrete zone is monitored in a given borehole, and multiple interval wells designed to measure multiple discrete depth intervals at a single location. Whether a single riser or multiple interval well is installed, it is important that efforts focus on intervals less than 10 feet thick and be specific to a single saturated zone.

All monitoring wells should be designed and installed in conformance with site hydrogeology, geochemistry, and contaminant(s). While it is not possible to provide specifications for every situation, it is possible to identify certain design components. Figure 7.1 is a schematic drawing of a single-riser/limited interval well. The casing provides access to the subsurface.

The intake consists of a filter pack and screen. The screen allows water to enter the well and, at the same time, minimizes the entrance of filter pack materials. The filter pack is an envelope of uniform, clean, well-rounded sand or gravel that is placed between the formation and the screen. It helps to prevent sediment from entering the well. Installation of a filter pack and screen may not be necessary for wells completed in competent bedrock. The annular seal is emplaced between the borehole wall and the casing and is necessary to prevent vertical movement of ground water and infiltration of surface water and contaminants.

Surface protection, which includes a surface seal and protective casing, provides an additional safeguard against surface water infiltration and protects the well casing from physical damage.

DESIGN OF MULTIPLE-INTERVAL SYSTEMS

It is often necessary to sample from multiple discrete intervals at a given location if more than one potential pathway exists or a saturated zone is greater than 10 feet thick. Chapter 5 - Monitoring Well Placement discusses the concepts involved in selecting zones to monitor.

Multiple-interval monitoring can be accomplished by installing single-riser/limited interval wells in side-by-side boreholes (well clusters) or using systems that allow sampling of more than one interval from the same borehole (multi-level wells, well nests, or single-casing, long-screen wells). Multiple-interval monitoring may be useful to:

Determine the hydraulic head distribution.

Measure temporal changes in vertical hydraulic head.

Determine vertical contaminant distribution.

Provide long-term multilevel water quality monitoring.

TGM Chapter 7: Design and Installation 7-2 Revision 1, February, 2008

Figure 7.1 Cross-section of a typical single-riser/limited interval monitoring well.

TGM Chapter 7: Design and Installation 7-3 Revision 1, February, 2008

WELL CLUSTERS

When monitoring multiple intervals at one location, single-riser/limited interval wells are often installed in adjacent, separate boreholes. These well clusters can be used to determine vertical gradients when distinct differences in head exist. They may be used to monitor discrete zones or evaluate chemical stratification within a thick zone. If flow direction has been determined prior to installation, the shallow well should be placed hydraulically upgradient of the deeper well to avoid the potential influence on its samples caused by the presence of grout in the annular space of the deeper well.

MULTI-LEVEL WELLS

Multi-level wells allow sampling of more than one interval in a single borehole. These levels are isolated within the well either by packers or grout. Probes, lowered into the casing, can locate, isolate and open a valve into a port coupling to measure the fluid pressure outside the coupling or obtain a sample. Individual tubes run from sampling levels to the surface.

The use of multiple-level monitoring wells in Ohio has been limited due to: 1) cost of installation, 2) difficulty in repairing clogs, and 3) difficulty in preventing and/or evaluating sealant and packer leakage. Detailed workplans (including construction and installation, methods to measure water levels and obtain samples, references to situations where these types of wells have been used successfully, and advantages and disadvantages) should be submitted prior to installing multi-level systems.

Several systems are commercially available for obtaining multi-level monitoring of a single borehole. Most consist of casing or tubing with monitoring ports located at user-selected intervals. In one system, however, a lining containing intermittent sampling ports is placed in the borehole. The systems may be sampled with small diameter pumps and bailers, or using proprietary samplers that go with the monitoring system. See Nielsen and Schalla (2006) for more information on multi-level well systems.

NESTED WELLS

Nested wells involve the completion of a series of single-riser wells in a borehole. Each well is screened to monitor a specific zone, with filter packs and seals employed to isolate the zones. Nested wells are not recommended because they are difficult to install in a manner that ensures that all screens, filter packs, and seals are properly placed and functioning. It is more efficient to install single-riser wells for each interval to ensure that representative samples can be collected. Aller et al. (1991) indicated that individual completions generally are more economical at depths less than 80 feet. According to Nielsen and Schalla (2006), the cost of installing well clusters is comparable to the cost for nested wells. Well clusters can enable savings on sampling and future legal costs that may be necessary to prove the accuracy of nested wells.

TGM Chapter 7: Design and Installation 7-4 Revision 1, February, 2008

SINGLE-CASING, LONG-SCREEN WELLS

Single-casing, long-screen wells are monitoring wells that, in general, are screened across the entire thickness of a water-bearing zone. If purging is performed immediately before sampling, only composite water samples are yielded, which are not adequate for most monitoring studies. If natural, flow-through conditions can be maintained, vertical water quality profiles can be obtained with passive sampling techniques. Vertical profiling may be a cost effective initial assessment to determine the depth of final wells.

Long-screen wells are not appropriate for detection monitoring. Furthermore, these wells can allow cross-contamination between different zones and, therefore, should not be used in contaminated areas.

CASING

The purpose of casing is to provide access to the subsurface for sampling of ground water and measurement of water levels. A variety of casing types have been developed. Items that must be considered during well design include casing type, coupling mechanism, diameter, and installation.

CASING TYPES

Three categories of casing are commonly used for ground water monitoring, including fluoropolymers, metallics, and thermoplastics (Aller et al., 1991). All have distinctive characteristics that determine their appropriateness.

Fluoropolymers

Fluoropolymers are synthetic plastics composed of organic material. They are resistant to chemical and biological attack, oxidation, weathering, and ultraviolet (UV) radiation. They have a broad useful temperature range, a high dielectric constant, a low coefficient of friction, display anti-stick properties, and have a greater coefficient of thermal expansion than most other plastics and materials (Aller et al., 1991). Standard properties of the various materials have been provided by Aller et al. (1991).

The most common fluoropolymer used for monitoring wells is polytetrafluoroethylene (PTFE).

It can withstand strong acids and organic solvents and, therefore, it is useful for environments characterized by the presence of these chemicals. It maintains a low tensile strength, which theoretically limits installation of Schedule 40 PTFE to an approximate depth of 250 ft1. It is also very flexible, which makes it difficult to install with the retention of straightness that is needed to ensure successful insertion of sampling or measurement devices. Dablow et al.

(1988) found that the ductile nature of PTFE can result in the partial closing of screen slots

1 The maximum depth for PTFE casing depends on site hydrogeology. If the casing largely penetrates unsaturated soils, the depth may be limited to approximately 100 feet. However, if the casing is placed mostly in water-bearing zones, then depth may be as great as 375 feet.

TGM Chapter 7: Design and Installation 7-5 Revision 1, February, 2008 due to the compressive forces of the casing weight. This makes slot size selection very difficult. PTFE is costly, generally ten times more expensive than thermoplastics. Studies by Gillham and O’Hannesin (1990), Parker et al. (1990), and Parker and Raney (1993) (in Nielsen and Schalla, 2006), found that PTFE showed higher sorption rates than PVC of organic compounds. These studies concluded that PVC was a better material to use when organics are present.

Metallics

Metallic materials include low carbon, carbon, galvanized, and stainless steel. Metallics are very strong and rigid and can be used to virtually unlimited depths. Corrosion problems are the major disadvantage for low carbon, carbon, and galvanized casings, as electrochemical and chemical attack alters water sample quality. U.S.EPA (1992) has listed the following as indicators of corrosive conditions (modified from Driscoll, 1986):

Low pH (< 7.0).

Dissolved oxygen exceeds 2 ppm.

Hydrogen sulfide in quantities as low as 1 ppm.

Total dissolved solids (TDS) greater than 1000 ppm.

Carbon dioxide exceeds 50 ppm.

Chloride (Cl-), bromide (Br-), and fluoride (F-) content together exceeds 500 ppm.

According to Barcelona et al. (1983), flushing before sampling does not minimize the bias of low carbon steel due to the inability to predict the effects of disturbed surface coatings and corrosion products accumulated at the bottom of the well. Due to their high corrosion potential, all metallics except stainless steel are unacceptable for monitoring wells.

Stainless steel is manufactured in two common types, 304 and 316. Type 304 is composed of iron with chromium and nickel. Type 316's composition is the same as Type 304's, but includes molybdenum, which provides further resistance to sulfuric acid solutions. Stainless steel is readily available in a wide variety of diameters.

Stainless steel can perform quite well in most corrosive environments. In fact, oxygen contact develops an external layer that enhances corrosion resistance (Driscoll, 1986).

However, several studies cite the formation of an iron oxide coating on the surface of stainless steel casing that forms in long-term exposure to ground water that can have unpredictable effects on the adsorption capacity of the casing material (Nielsen and Schalla, 2006). Under very corrosive conditions, stainless steel can corrode and release nickel and chromium into ground water samples (Barcelona et al., 1983). Combinations and/or extremes of the factors indicating corrosive conditions generally are an indication of highly corrosive environments. For example, Parker et al. (1990) found that both 304 and 316 showed rapid rusting (<24 hrs.) when exposed to water containing chloride above 1000 mg/l, and a study by Oakley and Korte (in Nielsen and Schalla, 2006) noted corrosion of stainless steel at even lower chloride levels (600-900 mg/L). Like PTFE, stainless steel is relatively expensive in comparison with thermoplastics. Nielsen and Schalla (2006) and Aller et al.

(1991) provided additional information on the properties of stainless steel.

TGM Chapter 7: Design and Installation 7-6 Revision 1, February, 2008

Thermoplastics

Thermoplastics are composed of large, synthetic organic molecules. The most common type used for monitoring wells is polyvinyl chloride (PVC), while a material used less often is acrylonitrile butadiene styrene (ABS). These materials are weaker, less rigid, and more temperature-sensitive than metallics. Thermoplastics are very popular due to their light weight, high strength to weight ratio, low maintenance, ease of joining, and low cost.

Common, acceptable PVC types are Schedule 40 and Schedule 80. The greater wall thickness of Schedule 80 piping enhances durability and strength, provides greater resistance to heat attack from cement, and allows construction of deeper wells. Only rigid PVC should be used for monitoring wells. Flexible PVC is composed of a high percentage of plasticizers (30 - 50%), which tend to degrade and contaminate samples (Jones and Miller, 1988). All PVC casing should meet Standard 14 of NSF International. This standard sets control levels for the amount of chemical additives to minimize leaching of contaminants (NSF International, 1988). Additional specifications have been provided by Nielsen and Schalla (2006) and Aller et al. (1991).

Drawbacks of PVC include brittleness caused by ultraviolet (UV) radiation, low tensile strength, relative buoyancy in water, and susceptibility to chemical attack. It is immune to corrosion and is resistant to most acids, oxidizing agents, salts, alkalies, oils, and fuels (NWWA/PPI, 1981). Additionally, Schmidt (1987) showed that no degradation of PVC occurred after six months immersion in common gasolines. However, studies have shown that high concentrations (parts-per-thousand or percentage concentrations) of tetrahydrafuran, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexane degrade PVC (Nielsen and Schalla, 2006). Barcelona et al. (1983) reported that low molecular weight ketones, aldehydes, amines, and chlorinated alkenes and alkanes may cause degradation.

Studies by Ranney and Parker (1995, 1997) and Parker and Ranney (1994b, 1995, 1996), showed that PVC is degraded when exposed to higher concentrations (0.2 and 0.4, or 20% and 40% of the solubility limit of the solvent in water) of aromatic hydrocarbons, aromatic and aliphatic chlorinated solvents, ketones, anilines, aldehydes and nitrogen-containing organic compounds. It is recommended that PVC not be used in situations where the material may be exposed to concentrations of known solvents or swelling agents of PVC greater than 25% of the solubility limit of the solvent or swelling agent (Nielsen and Schalla, 2006).

TYPE SELECTION

Many regulated parties choose PVC casing because of its lower cost; however, well integrity and sample representativeness are more important criteria. The high cost of analysis and the extreme precision of laboratory instruments necessitate the installation of wells that produce representative samples. Above all, the burden of proof is on the regulated party to demonstrate that casing is appropriate. The proper selection can be made by considering casing characteristics in conjunction with site conditions.

Casing characteristics include strength, chemical resistance, and chemical interference potential. The strength must withstand the extensive tensile, compressive, and collapsing forces involved in maintaining an open borehole. Since the forces exerted are, in large part, TGM Chapter 7: Design and Installation 7-7 Revision 1, February, 2008 related to well depth, strength often is important when planned depth exceeds the maximum range of the weakest acceptable material (100 to 375 ft. - PTFE). In these instances, either stainless steel or PVC should be chosen. Strength can be the overriding factor because the concern for chemical resistance and interference become insignificant if an open borehole cannot be maintained. Nielsen and Schalla (2006) provided specific strength data for commonly used materials.

The casing also must withstand electrochemical corrosion and chemical attack from natural ground water and any contaminant(s). Chemical resistance is most important in highly corrosive environments, when contaminants are present at extremely high levels, and when wells are intended to be part of a long-term monitoring program. For extended monitoring in corrosive environments, PTFE and PVC are preferred over stainless steel because of the potential for the metallic material to degrade. If high concentrations of organics (parts per thousand) are present, either PTFE or stainless steel should be selected.

PVC should not be used if a PVC solvent/softening agent is present or the aqueous concentration of a solvent/softening agent exceeds 25% of its solubility in water. It is suitable in most situations where low (parts per billion to low parts per million) levels of most organic constituents are present (Nielsen and Schalla, 2006).

The casing also should not interfere with sample quality by adding (leaching) or removing contaminants. In most cases, the magnitude of this interference is a function of the ground water's contact time with the casing. The longer the contact, the greater the potential for leaching and sorption. Various studies have been conducted [Barcelona and Helfrich (1988), Curran and Tomson (1983), Gillham and O'Hannesin (1990), Jones and Miller (1988), Miller (1982), Parker and Jenkins (1986), Parker et al. (1990), Reynolds and Gillham (1985), Schmidt (1987), Sykes et al. (1986), Tomson et al. (1979), Hewitt (1992, 1994), Parker and Ranney (1994)] to compare the sorbing and leaching characteristics of the three favored materials. No conclusive results have been obtained to indicate that any one is best. Most of these studies involved contact lasting days, weeks, and even months and, therefore, the results cannot be correlated to field conditions where contact is often minimal because sampling is generally conducted soon after purging.

In many cases, concern about sorption or leaching may be exaggerated. Barcelona et al.

(1983) and Reynolds and Gillham (1985) both concluded that the potential sorption biases for casing may be discounted due to the short contact after purging. Also, Parker et al. (1990) indicated that sorption of various constituents never exceeded 10 percent in the first 8 hours of their tests. They concluded that, on the basis of overall sorption potential for organic and inorganic compounds, PVC is the best compromise.

In summary, the appropriate casing should be determined on a case-by-case basis. PVC is acceptable when free product is not present and the solubility limits of organic contaminants are not approached (e.g., levels that exceed 0.25 times the solubility). Ohio EPA recognizes the difficulty inherent in establishing a "cut-off" level for when aqueous concentrations of organics cause failure of PVC. To be certain that casing will retain integrity, particularly when monitoring is planned for long periods of time (e.g., 30 years), Ohio EPA may recommend a more resistant casing when aqueous concentrations are relatively high but still below the criteria mentioned above.

TGM Chapter 7: Design and Installation 7-8 Revision 1, February, 2008

HYBRID WELLS

Casing not in contact with the saturated zone generally is not subject to attack. Therefore, it may be possible to install less chemically resistant material above the highest seasonal water level and more inert material where ground water continually contacts the casing. Such a "hybrid well" commonly is installed to reduce costs. For example, when monitoring a zone with high concentrations of organics, stainless steel could be installed opposite the saturated materials, while PVC could be used opposite the unsaturated materials.